TRAINING

REPORT

Guru Nanak Dev Thermal Power Plant Bathinda

Submitted by:

Yogesh Kumar-UE99078

BE Mechanical

ACKNOWLEDGEMENT

Myself YOGESH KUMAR a 3rd year student of UIET,PU CHD. express

my deepest gratitude to all who contributed in imparting me the valuable

knowledge during my training.

I am thankful to the Chief Engineer/Administration, GNDTP who provided

me the opportunity to undergo training .

With the help and valuable time of all the people I would not have been able

to learn and gather various important aspects of the MECHANICAL works

during my training.

Finally,yet importantly,I would like to express my heartfelt thanks to my

beloved parents for their blessings,my friends/classmates for their help and

wishes for the successful completion of my training.

INDEX

1. ORAGAZNISATION : AN INTRODUCTION

2. FUNCTIONAL DESCRIPTION

3. 6.6 KV CIRCUIT BREAKERS

4. MOTOR

a. H.T.MOTORS

b. L.T MOTORS

5. TRANSFORMERS

6. SWITCH YARD COMPONENTS

7. TURBO GENERATOR

ORANISATION:-AN INTRODUCTION

Thermal power stations require a number equipments performing a number

of complex processes with the ultimate aim to convert chemical energy of

coal or oil to electrical energy. This involves the generation of steam in

boiler by burning coal and /or oil. The steam in turn drives the turbine. The

generator coupled with the turbine produces electricity 11 kv which is

stepped u 220kv with the help of transformers and is fed into grid station

through transmission lines.

INTRODUCTION

Cheap and abundant supply of electric power is the major factor in the

development and progress of country.Punjab power sector comprises three

wholly state-owned corporations vizThe Guru Nanak Dev Thermal Plant

,Guru Hargobind Thermal Plant and Guru Gobing Singh Super Thermal

Power Plant which are responsible for power

generation,transmission,distribution and trading in the state.

LOCATION:

The Guru Nanak Dev Thermal Plant ( ਥ ਮਲ ਲ )at

Bathinda is one of the three thermal power stations in Punjab (the other

being at Lehra Mohabat and Ropar) .It is a medium-sized power station with

four units that were begun to be built in early 1970s and completed in 1982.

All total generate up to 440 Mw of power that meets the mammoth irrigation

needs of lower Punjab.

At couple of years back the Thermal Plant's functioning, which some claim

is not up to contemporary environment safety standards, has given birth to

serious health problems, not only in Bathinda itself, but also nearby towns

and villages, especially fly ash problem.

Input &outputs

There are three major inputs or raw materials required for the type of

thermal power station these are:

1. WATER

2. FUEL OIL

3. COAL

1. WATER:-

The raw water required for the thermal power station has been taken from

BATHINDA CANALS through a channel. This water is lifted by RAW

WATER PUMPS and fed into clarifiers to remove the turbidity of the

water.The clean water is stored in CLEAR WELLS from there it is sent to

WATER TREATMENT PLANTS,COOLING WATER SYSTEM AND

SERVICE WATER SYSTEMS.

The water in the WATER TREATMENT PLANT Is FILTERED and

DEMINERALISED WATER (D.M water) is stored in bulk storage tanks for

use in boiler and turbine .The cool water for condensation of steam is

circulated with the help of condensate water (C.W) PUMPS through

COOLING TOWERS. The hot water from the outlet of the condenser is

sprayed in the cooling tower to reduce its temperature. Some part of it is

used in cooling various auxiliaries in plant through BEARING COOLING

WATER PUMPS.

2. FUEL OIL:-

In this power house three type of fuel oil are used for preheating and at

low load of the boiler due to less problem faced in ignition of oil rather than

coal. These three types are:

1. High speed diesel oil.

2. Heavy furnace oil.

3. Low sulpher heavy stock.

The high speed diesel oil reaches power station by LORRY TANKERS.

The oil is decanted through pumps and team heating H.F.O& L.S.H.S is

stored in BULK STORAGE TANKS. The H.F.O&L.S.H.S comes to site

through rail tankers. As this oil is viscous, it is heated with steam and

decanted with pumps. The oil is stored in bulk storage tanks with steam

heating coil .H.F.O & L.S.H.S is burnt in the furnace of boiler after

atomizing with steam.

3. Coal

The coal reaches the power station in RAILWAY WAGONS.The daily

consumption of coal in stage-I is about 1500 M tonnes.The unloading of the

coal from railways wagons is done mechanically by tilting the wagon by

WAGGON TIPPLER. The coal is then sent to COAL CRUSHER by

conveyor belts. The crushed coal is then sent either to coal mill bunkers or

storage yard. The coal is also transported to coal bunkers from storage yard.

The coal is also transported to coal bunkers from storage yard through

conveyor belt when the coal wagons are not available. The crushed coal

stock from the mill bunker goes to coal mills through RAW COAL

FEEDERS where it is further pulverized to power form & is then transported

to the furnace of the boiler with the help of PRESSURED AIR from

PRIMARY AIR (P.A.) FANS.

FUNCTIONAL DESCRIPTION

The thermal power station burns fuel & uses the resultant to make the

steam, which derives the turbo generator. The fuel i.e. Coal is burnt in

pulverized form. The pressure energy of the steam produce is converted into

mechanical energy with the help of turbine. The mechanical energy is fed to

the generator where the magnets rotate inside a set of stator winding & thus

electricity is produced. In India 65% of total power is generated by thermal

power stations. To understand the working of the thermal power station

plant, we can divide the whole process into following parts:

COAL FLOW:

In coal fired plants, raw materials are air &water. In GNDTP, coal is

transported through railway wagons from m\s. coal India & is kept reserved

on a buffer stock. The brought out to the station is unloaded with the help of

wagon tippler. After unloading, the coal is sent to crusher house with the

help of conveyor belts. The coal which is now reduced to very small pieces

is sent to the coal bunkers with the help of conveyor belt .The raw coal is fed

to coal mills through raw coal feeders. Raw coal feeders basically regulate

raw coal to pulverize mill. The raw coal is fed to the furnace with the help of

primary fan through pulverized coal pipes. A portion of the primary air is

Heated utilizing the heat of the flue gases & then mixed with the cold air as

per requirement by the pulverized coal. Normally the temp. is maintained at

60 to 70 degrees. The coal is now burnt in the furnace using oil in the

beginning, showered through the nozzles at different elevations in the

furnace. To provide air for combustion, the heat of the flue gases also heat, if

the heat produced due to combustion is utilized for the conversion of water

into steam. This water is stored in the boiler drum. There are two sets of

pipes attached to the drum, one called riser & other known as down corner

through which the water comes to the ring header & steam moves up due to

the density difference of water & steam. This steam is super heated using

super heaters & meanwhile the flue gases are through out in the atmosphere

through chimney.

2. STEAM FLOW:

The super heated steam is sent to the turbine through pipelines. There

are three turbines in the units, using this steam at different temp & pressures.

After passing through high pressure turbine the steam is send to the reheater

for raising the temp. Of the steam after reheating the steam is sent to the

intermediate pressure turbine through reheated line. Here it losses most of its

temp. & pressure, & finally sent to low pressure turbine. The use of three

different turbines helps in increasing the efficiency of the Plant. The turbine

in turn connecting with a generator produces electricity. Then this electricity

is step up to 220 Kv with the help of step up transformer & supplied to

various substations/grids.

Meanwhile, the steam through low pressure (L.P.) turbine is condensed and

the condensed water is stored in hot well.

3. WATER FLOW:

The condensed water is extracted from the hot well through condensate

extraction pumps & sent to the boiler drum with the help of boiler feed

pump (B.F.P.) before passing through low pressure heater and deaerator.

While loss in water is make up from C.S. tank, which have D.M. door in it.

The C.S tank is directly connected to hot well.

The water used in condenser is sent to cooling tower for cooling. After

cooling this water is again sent to condenser with the help of Acirculating

water pump. The loss is making from raw water pump house through

clarifier pump house.

EXPLANATION OF LAYOUT DIAGRAM

1 WAGON TIPPLER:-

The coal may be transported to the plant site by rail wagons. The coal is

unloaded at the plant site mechanically by means of wagon tipplers. The

loaded wagon is emptied by tippling it in the underground coal hopper

from where the coal is carried by belt conveyer to the crusher house.

2.CRUSHER:

Coal unloaded by wagon tippler is carried to crusher house conveyors

for crushing. Here the coal is crushed to a size of 20mm.the crushed coal

is then supplied to boiler raw coal bunkers. The surpluse coal is carried to

coal storage area by means of belt conveyors. Crushing of coal is

essential for its optimum pulverizing and safe storage.

3 COAL MILLS:

In it small pieces of coal are converted into pulverized form. They are 6

in number.

4. FURNACE:-

It is the chamber in which fuel burns & fire blows. In addition it provides

support and enclosures for the combustion equipments i.e burners.

5.BOILER DRUM:-

A steam generator or a boiler is a combination of systems and

equipment in which the chemical energy of fossil fuels is converted into

thermal energy which is then transferred to a working fluid so as to

convert it into steam at high pressure and temperature. This high pressure

and temperature steam is then used for the development of power in a

turbine.

6.ELECTROSTATIC PRECIPITATOR:-

In this we have electrodes which attracts fly ash and extract it from flue

gases so that it can not enter atmosphere.

7 CHIMNEY:-

The flue gases from the boiler after removal of the fly ash in the

precipitators,are let off to atmosphere through boiler chimney.

8. TURBINE:-Turbine is the part which revolves due to steam pressure.

It is of three types:

a).HIGH PRESSURE TURBINE

b).INTERMEDIATE PRESSURE TURBINE.

c).LOW PRESSURE TURBINE.

9. TURBOGENERATOR:-It is the main machine which produces 110

mw electricity. It is H2(hydrogen) gas cooled. Therefore it is contained in

cylindrical chamber.

10.CONDENSER:- It condense steam coming from low pressure

turbine(L.P.T.) to hot water. By removing air and other non-condensable

gases from steam while passing through them.

11.COOLING WATER (C.W.) PUMP :- This pump send water from

cooling tower to condenser.

12.COOLING TOWER:- It is used to cool the water its height is near

about 143.5 mtr. The hot water is led to the tower top and falls down

through the tower and is broken into small particles while passing over

the baffling devices. Air enters the tower from the bottom and flow

upwards. The air vapourises a small percentage of water, thereby cooling

water falls down into tank below the tower from where it is pumped to

the condenser and cycle is repeated.

13.RAW WATER PUMP HOUSE :- It supplies raw water to the boiler.

14.CLEARIFIER PUMP HOUSE:-The water from raw is clear at

clarifier by putting alum in it & filtering it & then supplied to the

condenser.

15.CONDENSATE EXTRACTION PUMP:- C.E.P.Pump is used to

extract the condense water from the hot well and supply to the deaerator

after passing through L.P. Heater& economiser, so that high pressure

steam in the cylinder can be created.

16.LOW PRESSURE HEATER:- It is used to increase the temperature

of water, in this way efficiency of system increases.

17.DEAREATER:- It is used to remove air from water, which is

entrapped in the water molecules. It very important part because the

entrapped air effect air drum badly.

18.BOILER FEED PUMP(B.F.P.):- It is the heaviest drive in the plant

& supply water to boiler drum from deaerator.

19.HIGH PRESSURE HEATER(H.P.):- In this temperature of water

increases, thus efficiency further increases.

20. ECONOMISER:- In this flue gases exchange heat to the water to

increase system efficiency, causes saving in fuel consumption(5 to 10%).

Economiser tubes are made up of steel either smooth or covered with fins

to increase the heat transfer surface area.

6.6 KV CIRCUIT BREAKER

A circuit breaker is a device which:-

1 Makes or breaks a circuit either manually or by remote control under

normal conditions.

2 Breaks a circuit automatically under fault conditions.

Thus a circuit breaker is just a switch which can be operated under

normal & abnormal conditions both automatic or manually. To perform this

operation, a circuit breaker is essential consisting of fixed and moving

contacts called electrodes. When a fault occurs on power system, the trip coil

of circuit breakers energized which pulls apart moving contacts, thus open

the circuit dc supply is used for the operation of circuit breaker. On the basis

of medium used for extinction the circuit breaker are classified as:

1 OIL CIRCUIT BREAKERS

2 AIR BLAST CIRCUIT BREAKER

3 SULPHER HEXAFLURID CIRCUIT BREAKER.

Oil circuit breaker

It is well known that when a circuit carrying a large current is broken, an arc

occurs at that point where the contacts are separate; the arching is specially

severe when high voltages are involved and if a short circuit occurs on a

high voltage cable which is supplied from large power station. The arc

would be powerful to bridge the contacts of the switch and destroy it by

burning. The device is employed as an oil breaker. An oil breaker posses

the property of always breaking an alternative current at its zero value.

These switches are suitable for a maximum voltage of 6.6 kv. The contacts

of these switches, which break high tension circuit, are immersed in oil to

ensure rapid & effective rapture of the circuit. When the arc occurs, the oil in

its path is vaporized and the gas thereby generated extract a pressure on the

surrounding oil. This pressure is utilized in arc controlled devices to cause a

movement of fresh cool oil across the path of the arc, thereby efficiently

assisting its interruption.

Pictorial diagram:

AIR BLAST CIRCUIT BREAKER

All air blast circuit breaker requires an auxiliary compressed air system

which supplies air to the breaker air receiver. When opening is required,

compressed air is admitted to the arc extinction chamber. It pushes away the

moving contacts. In doing so the contacts are separated and the air blast

takes away the ionized gases along with it and assists arc extinction. Air

blast circuit breaker extinguishes the arc. Within one or two cycle and arc

chamber is filled with a high pressure air, which prevents restrike.

SULPHER HEXAFLURID CIRCUIT BREAKER

In SF6 Circuit breaker SF6 gas is blown axially along the arc. The

heat is removed from the arc by axial convection and radial dissipation.

Consequently, the arc diameter reduces during the decreasing node of the

current wave. The diameter becomes small during current zero. Turbulent

flow is introduced around current zero for extinguish the arc. The above

diagram show the layout diag of SF6 circuit breaker.

.

MOTORS:-

HIGH TENSION MOTOR :

1 CIRCULATING WATER(C.W.P.) PUMP MOTORS:-

FUNCTION:- C.W. pump is used to circulate cooling water to the

condensers so that low pressure steam in the cylinder can be converted

into water.

2 CONDENSATE EXTRATION PUMP(C.E.P.) PUMP MOTOR:-

FUNCTION:-C.E.P. pump is used to extract the condense water from the

hot ll and supply to the deaerator after passing through L.P. Heater&

economiser, so that high pressure steam in the cylinder can be created.

3.BOILER FEED PUMP(B.F.P.) MOTOR:-

FUNCTION:-Its function is to supply the water to the boiler drum. It

takes water from the deaerator by creating strong suction. It is the biggest

motor in the plant.

4.COAL MILL MOTOR:-

FUNCTIONS:- Its function is to grind the coal pieces to fine powder

(pulverized) form i.e. upto size of 25 micron.

5 PRIMARY AIR FAN MOTOR:-

FUNCTION:- Its function is to carry pulverized coal from the coal mill

to the furnace for its ignition. It creates strong draft of air that carries

pulverized coal.

7). FORCE DRAUGHT (F.D.) FAN MOTOR:-

FUNCTION:-F.D. fan is used to supply fresh air to the furnace for the

proper ignition of coal into the furnace.

8). INDUCED DRAFT (I.D.) FAN:-

FUNCTION:-Its function is to discharge flue gases to the atmosphere

through the chimney after passing through the precipitation.

LOW TENSION MOTOR

1. B.C.W. DRAIN MOTOR:-

FUNCTION:-IT PUMP THE B.C. WATER TO THE PUMP.

2. SEAL WATER PUMP MOTOR:-

FUNCTION – It provides a layer of water to the lower position of boiler

in order to seal it from the entry of atmospheric air.

3.SEAL WATER VAPOUR EXHAUST FAN :-

FUNCTION- It prevents the entry of air bubbles in the turbine cylinder

by providing the opposite push.

4. CENTIFUGE PUMP MOTOR –

FUNCTION – To centrifuge the vapour that enters by change in turbine

an remove them.

5 ASH SULRRY PUMP MOTOR: –

FUNCTION – To pump ash slurry to the ash disposal area.

6. EMERGENCY OIL PUMP(A.C): –

FUNCTION – To provide oil to the shaft and bearing of the turbine if

seal oil pump and taking oil pump fails.

7. RAW WATER MOTOR PUMP:

FUNCTION- It is use to pump raw water from the lake to the plant.

8. INSTRUMENT AIR COMPRESSOR:-

FUNCTION- It is used to compress the air used to control pneumatic

controlled instruments at pressure 6 to 7 kg/cm cube.

9. SERVICE AIR COMPRESSOR:-

FUNCTION- Its function is similar to instrument air compressor.

10.CLARIFIER WATER PUMP MOTOR-

FUNCTION- It pump the filtered water from clarifier to D.M. water

treatment plant.

TRANSFORMERS

The transformer is the most convenient & economical device for transfer of

power from one voltage to another voltage at the same frequency. It works

on the principle of electromagnetic induction. There is hardly any

installation without a transformer. Due to this equipment, it has been

possible to transmit bulk power to load centers from far off power houses

and to various machineries and switchgears of the power plant. Transformers

are of two types:-

#STEP-UP TRANSFORMER - which step-up the voltage at secondary side

called step-up transformer.

#STEP-DOWN TRNSFORMER- which step-down the voltage at secondary

side are called step-down transformer.

MAIN PARTS OF POWER TRANSFORMERS

# PRIMARY WINDING

# SECONDRY WINDING

# OIL TANK

# DRAIN COKE

# CONSERVATOR

# BRETHER

# TUBES FOR COOLING

# TRNSFORMER OIL

# EARTH POINT

# EXPLOSION VENTS

# TEMPERATURE GAUGE

# BUCHHOLZ RELAY

# PRIMARY TERMINALS

# SECONDARY TERMINALS

SOME ACCESSORIES OF TRANSFORMERS ARE

DESCRIBED BELOW:-

1.OIL CONSERVATOR:-

Oil conservator is a short of drum mounted on the

top of transformer. A level indicator is fixed to it, which gives alarm at low

level. Conservator is connected through a pipe to the transformer tank

containing oil. This oil expands & contract depending upon the heat

produced & so the oil level in conservator is left open to the atmosphere

through a breather so that the extra air may go out or come in.

2. BREATHER:

The breather is a box containing calcium chloride or silica

gel to absorb moisture of our entering the conservator as it is well known

fact that the insulating property of the transformers oil is lost if a small

amount of moisture enter in it. So dry air is allowed to pass through the

breather.

When oil level in oil conservator changes, air moves in &

out of the conservator. This action is known as breathing. Dry silica gel is of

the blue color. It turns pale pink as it absorbs moisture. The wet silica gel

can be regenerated by drying.

3.BUCHHOLZ RELAY:-

This relay is a gas-actuated relay which is meant for

the protecting of oil immersed transformer from insulation failure, core

heating or any type of internal fault which may cause the heating of oil

beyond the specified temp.. Due to any internal fault, oil is heated –up & oil

vapours so formed causes either the alarm circuit(for less fault) or trip the

circuit(for sever fault).

4.EXPLOSION VENT:-

It is also a safety device of the transformer which

protects the transformer tank from gases induced by & any type of short

circuit in the transformer. This consists of a vertical pipe closed by a

diapharm made of thin bakelite sheet. This diapharm burst or slides out in

case of abnormal pressure inside the tank. A diverter plate is used at the

bottom of the explosion vent to ensure that gases produce inside the

transformer are directed toward the buchholz relay & don’t get collected

inside the ventilation and equalize the pressure on each side of the diverter

plate.

5. TEMP. INDICATOR:-

It is also a protective device fitted to the transformer to indicate temp.of

transformer oil. For measuring temp. Of the oil, bulb of the vapour pressure

type thermometer is placed in the hot oil & dial of the thermometer is

mounted outside the tank. Two indicating pointers black and red are

provided. Alarm contacts are also provided which come into action when

predetermined permissible higher temperature is reached under abnormal

operating conditions.

6. BUSHING: –

The bushing serves as supports and insulation of the bus bars and

transformer terminal. The bushing consists of porcelain shell body, upper

and lower locating washer used for fixing the position of bush bar and

mounting flange with the hole drilled for fixing bolt and it is supplied with

an earthing bolt.

7.MAGANETIC OIL GAUGE:-

The magnetic oil level gauge supervises the level of oil in the conservator

tank. The oil level gauge is provided on the transformer are of dial type with

minimum and maximum level marking and a pointer which indicate the

level of oil in the conservator. Sometime the scale is also graduated for oil

temperature on the basis of its level.

8.TAP CHANGER:–

The voltage control of transmission

And a distribution system is obtained by tap changer. Tap changer are either

on load or off load tap changer. Tap changer is fitted with the transformer

for adjusting secondary voltage.

IMPORTANT TRANSFORMERS IN THE PLANT

1. GENERATOR TRANSFORMER ( 11KV/220 KV)–

It converts 11 kv to 220 kv which is supplied from generator to 220kv and

supplied it to the bus bar/ grid.

2.STATION SERVICE TRANSFORMER (40MVA, 220KV/7KV) –

It converts 220kv which is coming to station from BBMB to 7kv and fed to

station auxiliary.

3. UNIT AUXILIARY TRANSFORMER ( 11KV/6.6KV) –

It converts 11kv which is supplied from generator and step down to 6.6kv to

fed unit auxiliary. The unit auxiliary transformers are of two in no.

The above three transformers are main transformers use in the plant. And

special care is taken for the safety of the transformer. Time to time various

tests is done for the safety of transformer.

SWITCHYARD COMPONENTS

1.SWITCH-GEAR-

Switch gear is a control switch that

Control the operation of a power circuit. The two function of a switch in

power systems are –

I). To permit the transmission lines to be convenient put into and taken out

from service.

Ii). To disable the some plant and lines when these become faulty, to be

rapidly and safely isolated by automatic means.

The first of these can be served by relatively simple switches the

second however require circuit breakers, which are more robust & capable of

breaking the large value of fault power that results in faults on major power

system. Since all plants and lines are liable to develop faults as results of

mechanical damage, electrical breakdown, errors in operation etc. The

simple isolators switch in favour of automatic circuit breakers even for

switching function. The whole switchgear assembly consists of two parts:-

1. PANEL- Panel consists of protective relays, mounting of potential

transformer, current transformer, ammeter, voltmeter & energy meter. The

potential transformer is mounted on the panel. The primary is connected to

11kv & the reduce voltage from the secondary is given to energy meter as

line voltages & for protective purposes.

2.TROLLY- The trolley consists of current carrying contacts called

electrodes. These are normally engaged but in predetermined conditions,

separate to interrupt the circuit, when the contacts are made.

BUS BAR ARRANGEMENT

Conductors to which a number of circuits are connected called bus – bars. In

power plants, shut down results disconnection of supply to a large area.

Hence to avoid shut down the major plants should have elaborate bus bar

arrangement with duplicate buses, alternative supply arrangement section

etc. the extra high voltage equipments such as isolators, circuit breaker are

generally costly hence unnecessary equipment should not be provided.

SINGLE BUS BAR ARRANGEMENT:-

The single arrangement consists of a single (three phase) bus bar to

which various feeders are connected. In case of fault or maintenance of

bus, the entire bus bar has to be de-energized and the total shutdown

results. This scheme is most economical and simple.

DOUBLE BUS BAR ARRANGEMENT:-

The double bus systems provide additional flexibility, continuity of

supply and permit periodic maintenance. In the event of fault on the

bus bar the other can be used the figure shows to the bus bar

arrangement. There are two buses called main bus and reserve bus.

The coupler can be closed so as to connect two buses while

transferring the power to the reserve bus.

Closed bus coupler, the two buses are now at same potential.

Closed isolator on reserve bus.

Open isolator on main bus.

LIGHTING ARRESTER

A lighting arrester is device, which proves low impedance path for the

flow of current between the line and earth when the systems voltage

increases more than the desire value and regains its original properties of an

insulator at normal voltage. It is connected between line and earth at the

switch yard near the transformer.

The lighting arresters are extensively used for protection of

transformers, switch gears and electrical equipments of over head lines,

power houses and sub-station . These are also use to protect the line and

equipments from sky lighting.

TURBO GENERATOR

GENERAL:- Modern features of direct cooling by water & hydrogen are

incorporated in the turbo generator, thus evolve an economical & reliable

design. The machine is provided with a fast acting excitation system &

dependable auxiliary service to give prolonged trouble free operation over

the years. All the material that goes into the manufacture of this machine

subjected to various test as per national & international standards. Each

component undergoes series of stage wise tests. Description of various parts

is given below:-

1. STATOR WINDING AND INSULATION:- The stator has a three

phase, double layer, short chorded, bar type winding, having two parallel

pats . Each coil side consists of glass insulated solid and hollow conductors

with cooling water passing through the patter. The elementary conductors

are rebel transposed in the slot portion of winding to minimize eddy current

losses.

Adequate protection is provided to avoid corona & other discharges. In the

slots, the sides are firmly held in the position by fibrous slot wages, which

are mechanically strong and have high dielectric properties. The overhang

portion of the coil is securely lashed with glass chord to bondage rings&

special buckets of non magnetic steel, which are in turn, fixed to the core

press rings. On short circuits the forces between the conductor tend to open

the cone formed by overhang portion of the coils, but the movement is

effectively presented by supports & lashings.

2. DISTILLATE HEADERS OR STATOR WATER HEADER: -

ring type water heads, made of copper are provided separately for distillate

inlet & outlet in the stator on turbine side. The headers are supported on

insulators and isolated from stator body. The winding ends are solidly

soldered into the coil lugs which are than ultrasonically tested. Individual

bars are provided with water inlet/outlet connections made of P.T.F.E.

houses. The bar heads are insulated by fiber molded corners. The winding

scheme along with the water connections. The complete water path assembly

is subjected to the rigid hydrolytic pneumatic tests at various stages to

ensure water tightness and to detect blocking of the flows paths.

3. TERMINAL BUSHINGS:-

Water cooled terminal bushings are housed in the lower part of the stator on

the slip ring side. Porcelain insulators are provided to insulate the terminal

bars from the stator body. Effective sealing is provided between the terminal

bushing and the stator body to avoid any possibility of leakage of hydrogen.

Terminal bushing is housed inside a chamber made of non magnetic steel

plates. Three phase terminals are brought out to facilitate external

connections. The terminal plate of the end terminals, where bus bar

connections are made is silver plated.

The terminal bushings can be replaced without removing the stator from

foundation. Provision is made for fixing the external bus ducts with the

terminal plate.

4. ROTOR: -

The rotor is of cylindrical type shaft and body being forged in one piece

from chromium, nickel, molybdenum & vanadium steel. Prior to matching, a

series of comprehensive ultrasonic examination and other tests are carried

out on rotor body and shaft portion to ensure of any internal defects. The

rotor with all the details assembled, dynamically balanced to a high degree

of accuracy and subjected to 20% over speeding for 2 minutes ensuring

mechanical strength.

5. FIELD WINDING:-

The field winding is made from hard drawn silver bearing copper. Rotor

winding is held in position against centrifugal forces by duralium forces

wedges in the slot portion & by non magnetic steel retaining rings in the

over hang portion. Gap pick up system is employed for direct hydrogen

cooling of rotor winding. Several groups of ventilation ducts are mulled on

the sides of the rotor coil for gas passage. The rotor slot wedges are of

special profiles with elliptical holes rolled in to match the ventilation ducts

on the winding stacks. The end windings are insulated from rings with the

help of glass epoxy molded segments. Copper segmental type damper

winding is provided in the end zone of rotor to prevent over heating of

returning ring s during asymmetrical & asynchronous operation.

6. SHAFT MOUNTED FANS:-

For circulating the cooling gas inside the generator, two propeller type fans

are shaft mounted on this & of rotor body. Fan hubs are made from alloy

steel forging and are hot fitted on the rotor shaft with sufficient interference.

The alloy steel cast fan blades are machined in the tail portion to suit the fan

hub and held in position with the help of conical pins. The blades can be

easily removed from or assembled in the fan hub. Fan shields fixed to the

end shields, guide the flow of gas through the fan sections.

7. SLIP RINGS:-

The slip ring consists of helically grooved alloy steel rings shrunk on the

rotor shaft & insulated from it. For convenience in assembly both the rings

are mounted on a single, common steel bush, which has an insulated jacket

pre molded on it. The complete bush with slip ring is shrunk on the rotor

shafts. The slip rings are provided with inclined holes for self-ventilation.

The helical groove cut on the outer surface of the slip rings improves brush

performance